Design and performance of an ionisation chamber for the measurement of low alpha-activities

A new ionisation chamber for alpha-spectroscopy has been built from radio-pure materials for the purpose of investigating long lived alpha-decays. The measurement makes use of pulse shape analysis to discriminate between signal and background events. The design and performance of the chamber is described in this paper. A background rate of (10.9±0.6)countsperday in the energy region of 1-9 MeV was achieved with a run period of 30.8 days. The background is dominantly produced by radon daughters.